1. Field of the Invention
The present invention relates to a simple and advantageous process of producing N,N-dimethylamino methane diphosphonic acid. Said acid is distinguished from the known amino alkane diphosphonic acid by its superior properties, more particularly its superior inhibitory effect on scale and deposit formation in aqueous systems and its anticorrosive activity. For this reason it has proved to be useful for many purposes.
2. Description of the Prior Art
A number of processes to produce amino alkane diphosphonic acids are known. Amino alkane diphosphonic acids are obtained according to German Offenlegungsschrift No. 1,958,123 by reacting monocarboxylic acid amide with phosphorus trihalogenides and subsequently hydrolyzing the resulting reaction product. Working with phosphorus halogenides especially with phosphorus trichloride, however, has a number of disadvantages.
It is known, for instance, that phosphorus trichloride reacts with small amounts of water such as they are encountered as traces of moisture in any apparatus which has not been dried thoroughly, and forms yellow, insoluble decomposition products. These impurities are causing considerable trouble especially when the phosphonic acid is precipitated in crystalline form in the reaction vessel already during the reaction. It is then necessary to again dissolve the precipitated phosphonic acid in order to separate the impurities. It is also well known to an expert that when carrying out the reaction on a semi-technical scale, there are formed frequently not only such insoluble decomposition products but also monomeric phosphine. Phosphine, however, is highly toxic and has a tendency to self-ignition. Therefore, specific precautionary measures must be taken when producing amino alkane diphosphonic acids according to the aforesaid process.
According to German published application No. 2,048,912 carboxylic acid amide dichlorides or dibromides are reacted with phosphorous acid whereby amino alkane diphosphonic acids are obtained. This process, however, is quite complicated because it requires additional process steps in order to produce the starting materials, the carboxylic acid amide dihalogenides.